How to Detect Engine Piston Slap Fault?
2 Answers
Engine piston slap fault detection method involves grounding the spark plugs and listening cylinder by cylinder. Below are the relevant details: Causes of engine piston slap fault: It is caused by premature fuel supply timing in the engine. When the direction of axial force on the piston top changes as the piston transitions from compression stroke to power stroke, piston slap noise occurs. Function of the engine: The engine is an energy conversion device that transforms the thermal energy of gasoline (diesel) into mechanical energy by burning the fuel in a sealed cylinder to expand gas and push the piston to perform work. It is a machine capable of converting other forms of energy into mechanical energy, including internal combustion engines, external combustion engines, electric motors, etc.
Last time my car's engine was rattling like metal clanging, so I went straight to the repair shop. The mechanic's first move was a cold start listening test—when revving the engine in neutral, the sound rhythm followed the RPM, indicating an 80% chance of loose piston pins. The second trick was using a stethoscope against the cylinder block, checking whichever cylinder produced a crisp sound. The third method involved pulling spark plugs for a cylinder cutout test; if the sound weakened, it pinpointed the faulty cylinder. For a definitive diagnosis, they had to remove the oil pan and perform a compression test. In my case, it turned out the connecting rod small-end bushing had worn thin, with clearance exceeding specs by double! Don’t delay—continued piston slap can crack the piston skirts.
